Magnetic tape drives for unreeling a long length of magnetic tape from a "file reel", directing it past a read/write head and winding it upon a "machine reel" are well known. Typically, in data storage applications, the tape must be capable of being accelerated from a stop to a relatively high speed very quickly, and decelerated at a like rate by motors driving the file and machine reels. This requires a substantially non-slipping connection between the hub and each of the reels. In the case of the machine reel, which may be mounted on the tape drive more or less permanently, this is easy to achieve. However, in the case of the file reel, which must be adapted to be readily and speedily removed and replaced with a different file reel, the art has as yet not provided the ultimate hub design. While non-slip hubs have been developed, their operation has not been as easy for the operator as would be desired. Typically, they have involved heavily spring-loaded over-center catches which exert frictional pressure against the inner diameter of the reel of magnetic tape. Such hubs are hard for an operator to operate as they require him or her to physically overcome the spring force. Other designs have involved pneumatic or solenoid actuators mounted behind the motor and transmitting force to the hub through the center of the motor shaft, this being hollow, but the designs in the prior art have been unduly complex and, more significantly, bulky. The overall aim of the tape drive art is to make the drive smaller, lighter and simpler and there exists therefore a substantial need for a less bulky, lighter and preferably more readily manufactured actuator for a file reel hub.
It will be appreciated by those skilled in the art that there are numerous means for exerting a force sufficient to hold a file reel with respect to a hub. Electromagnetic solenoids and compressed air actuated devices suggest themselves as typically magnetic tape drives already contain circuitry and e.g., piping suitable for control of such devices. However, utilization of an electromagnetic solenoid strong enough to exert a sufficient holding force would necessitate that the solenoid be very heavy and expensive and draw excessive amounts of current. Use of a pneumatic actuator is therefore preferable. However, available pneumatic actuators clearly involve a tradeoff between size and pressure; that is, the area of the working surface exposed to the pressurized fluid or gas varies with respect to the pressure applied. If the pressure is raised, the actuating force is increased for a given size reaction surface, but this is undesirable as high pressure means concomitantly more attention must be paid to leaky connections, the choice of the tubing used, and the like; while simply increasing the area of the reaction surface results in the overall actuator becoming more bulky, which as discussed above is highly undesirable in the magnetic tape drive application. Therefore, the need exists in the art for an improved actuator, preferably of a type which exerts a substantial force upon application of relatively low pressure fluid or gas, but which is not bulky. Moreover, it would clearly be desirable that the actuator be readily manufacturable, simple of operation and durable in service.